A typical wireless communication system includes a number of base stations each radiating to provide one or more coverage areas or “cells” in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices (whether or not “user” operated). In turn, each base station may sit as a node on a core access network that includes entities such as a network controller, switches and/or gateways, and the core network may provide connectivity with one or more external transport networks such as the public switched telephone network (PSTN) and the Internet. With this arrangement, a UE within coverage of a base station may engage in air interface communication with the base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Such a system may operate in accordance with a particular air interface protocol, with communications from the base stations to UEs defining a downlink and communications from the UEs to the base stations defining an uplink. Examples of existing air interface protocols include, without limitation, Long Term Evolution (LTE) (using orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), and BLUETOOTH. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handover between sectors, and other functions.
In practice, each cell in such a system may operate on one or more carrier frequencies and may be structured in accordance with the air interface protocol to define air interface resources for carrying communications between the base station and UEs. For instance, on the downlink, certain resources could be reserved to carry control signaling to UEs, other resources could be reserved to carry bearer data (e.g., application-layer communications) to UEs, and still other resources could be reserved to carry a pilot or reference signal that UEs can detect and measure as a basis to evaluate coverage. And on the uplink, certain resources could be served to carry control signaling from UEs, and other resources could be reserved to carry bearer data from UEs.
When a UE first powers on or enters into coverage of such a system, the UE could search for a strongest cell in which to operate and could then engage in signaling with the base station that provides that cell, and in turn with core network infrastructure, to register or attach for service. In turn, the UE could then be served by the base station in a connected mode or in an idle mode. In the connected mode, the UE may have a radio-link-layer connection with the base station, over which to communicate bearer data (e.g., application-layer data). And in the idle mode, the UE may lack a radio-link-layer connection but may monitor for pages and may transition to the connected mode when necessary to engage in bearer communication.
While so served, the UE may also monitor coverage strength from its serving base station and from adjacent base stations, to help ensure that the UE is served with sufficiently strong coverage and perhaps with the strongest available coverage. If the UE's coverage from its serving base station becomes threshold weak and if another base station's coverage becomes threshold strong (e.g., threshold stronger than the serving base station's coverage), the UE may engage in signaling with its serving base station, and the serving base station may take action to coordinate handover of the UE to the other base station.
Optimally, a wireless service provider will strategically implement base stations throughout a market area so that served UEs can transition between the base stations' coverage areas without loss of coverage. Each base station may include an antenna structure and associated equipment, and the service provider may connect each base station by a landline cable (e.g., a T1 line) with the service provider's core network, to enable the base station to communicate on that network.
In certain locations, however, it may be impractical for a wireless service provider to run landline connections to base stations. For instance, where a service provider seeks to provide many small coverage areas blanketing a market area or to fill in coverage holes between coverage of other base stations, the service provider may implement many small-cell base stations throughout the market area, but it may be inefficient or undesirable to run landline cables to every one of those small-cell base stations.
To provide coverage in such locations, the wireless service provider may instead implement relay base stations, which could be configured to operate in much the same way as a conventional landline-connected base station but could have a wireless backhaul connection to the core network. In particular, each relay base station could have an associated UE module, referred to as a UE-relay, which would be served by an existing base station of the network, referred to as a donor base station, with the air interface between the UE-relay and the donor base station defining a wireless backhaul connection for the relay base station. With this arrangement, the relay base station could thus conveniently communicate with the core network via the UE-relay, the wireless backhaul connection, and the donor base station.